The present invention relates to processes and apparatus for recovering, such as by distillation, dichlorohydrins from a mixture comprising the same such as the effluent generated by a process for converting multihydroxylated-aliphatic hydrocarbon compound(s) and/or ester(s) thereof to chlorohydrins.
Distillation is a well-known process for separating the components of a mixture according to their relative volatility. A liquid mixture is heated to a temperature sufficient to vaporize at least the component(s) to be separated, the vaporized component(s) is/are condensed at a location apart from (usually above) the liquid mixture, and the condensed component(s) are removed from the distillation process.
Distillation may be used to recover dichlorohydrins from a reaction mixture containing the same. Dichlorohydrins are useful in preparing epoxides such as epichlorohydrins. Epichlorohydrin is a widely used precursor to epoxy resins. Epichlorohydrin is a monomer which is commonly used for the alkylation of para-bisphenol A. The resultant diepoxide, either as a free monomer or oligomeric diepoxide, may be advanced to high molecular weight resins which are used for example in electrical laminates, can coatings, automotive topcoats and clearcoats.
Glycerin is considered to be a low-cost, renewable feedstock that is a co-product of the biodiesel process for making fuel. It is known that other renewable feedstocks such as fructose, glucose and sorbitol can be hydrogenolized to produce mixtures of vicinal diols and triols, such as glycerin, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol and the like. With abundant and low cost glycerin or mixed glycols, economically attractive processes for recovering dichlorohydrins from effluents produced by the above processes are desired.
A process is known for the conversion of glycerol (also referred to herein as “glycerin”) to mixtures of dichloropropanols, compounds I and II, as shown in Scheme 1 below. The reaction is carried out in the presence of anhydrous HCl and an acetic acid (HOAc) catalyst with water removal. Compounds I and II can then be converted to epichlorohydrin via treatment with caustic or lime.

Various processes using the above chemistry in Scheme 1 have been reported in the prior art. For example, epichlorohydrin can be prepared by reacting a dichloropropanol such as 2,3-dichloro-1-propanol or 1,3-dichloro-2-propanol with base. Dichloropropanol, in turn, can be prepared at atmospheric pressure from glycerol, anhydrous hydrochloric acid, and an acid catalyst. A large excess of hydrogen chloride (HCl) was recommended to promote the azeotropic removal of water that is formed during the course of the reaction.
WO 2006/020234 A1 describes a process for conversion of a glycerol or an ester or a mixture thereof to a chlorohydrin, comprising the step of contacting a multihydroxylated-aliphatic hydrocarbon compound, an ester of a multihydroxylated-aliphatic hydrocarbon, or a mixture thereof with a source of a superatmospheric partial pressure of hydrogen chloride to produce chlorohydrins, esters of chlorohydrins, or mixtures thereof in the presence of an organic acid catalyst. This process is also referred to herein as a “dry process”. Azeotropic removal of water in a dry process via a large excess of hydrogen chloride is not required to obtain high chlorohydrins yield. Separation of the product stream from the reaction mixture may be carried out with a suitable separation vessel such as one or more distillation columns among others. WO 2006/020234 A1 does not describe a specific distillation method and a method to minimize formation of heavy byproducts.
WO 2005/021476 A1 describes a process using atmospheric partial pressure of hydrogen chloride, acetic acid as the catalyst, and a cascade of loops, preferably three loops, each loop consisting of a reactor and a distillation column in which water of reaction, residual hydrogen chloride and dichloropropanol are removed from the reaction effluent. This process for distillation, requiring a cascade of reactor/distillation loops, is very expensive since the process requires several reactors/columns in the process. Furthermore, valuable acetic acid is lost with the distillate, needing to add more acetic acid to make up for the catalyst loss in distillation.
WO 2005/021476 A1 further describes that for the distillation under reduced pressure to separate the water of reaction any device for distillation can be used, such as various types of evaporators or distillation systems with various internals such as trays, packing and the like. WO 2005/021476 A1 does not distinguish between the various types of internals that can be used in the distillation regarding or the advantages of one type of internals versus another type of internals, i.e., all of the column internals are treated alike.
WO 2005/054167 A1, on page 16, describes recovery of dichloropropanol from glycerol hydrochlorination reaction effluent by distillation or evaporation. WO 2005/054167 A1 describes distillation conditions such as temperature and pressure or vacuum.
EP 1 752 435 A1 discloses another process for producing a chlorohydrin by reacting a multihydroxylated aliphatic hydrocarbon and/or an ester thereof and aqueous hydrogen chloride to produce chlorohydrins, esters of chlorohydrins, or mixtures thereof under atmospheric condition in which a purge from the reactor bottom is fed to a stripper. In the stripper partial stripping of most of the hydrogen chloride, the water from the aqueous hydrogen chloride reactant and the water that is formed during the course of the reaction (also referred to herein as “water of reaction”), from the reaction mixture is carried out and a distillation or stripping column is fed with the liquid phase from the stripper. The gas phase from the stripper, which contains most of the unreacted hydrogen chloride, the excess water from the aqueous hydrogen chloride reactant and the reaction by-product water from the reaction mixture, is conducted to a distillation column fed by the vapor produced by the reactor; or is recycled directly to the reactor.
The main fraction of dichloropropanol is collected from the top of the distillation or stripping column. The column residue is recycled to the reactor. This process (also referred to herein as a “wet process”), not only adds water via the aqueous hydrogen chloride reactant into the process, but also produces water of reaction in the process. The removal of a large excess of water in the wet process via a stripper is less energy efficient and unnecessary for a dry process. A better utilization of the stripper can be done in the recovery of dichloropropanol. This wet process also does not describe specific methods to minimize heavy by-product formation.
CN 101007751A describes another process that combines wet and dry processes with two reactors in series, in which a tubular reactor is used as the first reactor and a foaming-tank reactor is used as the second reactor. Aqueous hydrogen chloride is fed to the tubular reactor and gaseous hydrogen chloride is fed to the foaming-tank reactor. Inert impurities are added to the hydrogen chloride in order to improve the efficiency of stripping water from the reaction mixture in the foaming-tank reactor. CN 101007751A also does not describe specific methods to minimize heavy by-product formation.
EP 1 762 556 A1 describes a process for producing dichloropropanol by reacting a glycerol containing metal salt with a chlorinating agent in a reaction mixture. At least a fraction obtained from the reaction mixture, which contains metal salt, is subjected to a treatment comprising one or more separation operations to remove metal salt from said fraction. EP 1 762 556 A1 does not describe a process or an apparatus for reducing the formation of heavy byproducts during recovery of dichlorohydrins.
The inventor found that one or more component(s) of the reaction mixture fed to the distillation column according to the above processes form heavy byproducts during distillation requiring a purge from the process to prevent build up of the heavy byproducts in a continuous recycle process. WO 2005/021476 A1 describes processing a residue containing a mixture of undesired products but WO 2005/021476 A1 does not describe how to minimize formation of the undesired higher-boiling waste products during distillation. The heavy byproducts and the purge reduce recovery of dichlorohydrin(s) in a recycle process and increase cost related to non-utilizable byproduct waste disposal/conversion. Opportunities remain to further improve such distillation processes to reduce byproduct formation
Accordingly, it is desired to provide improved processes and apparatus for separating the product dichlorohydrin from the reaction effluent of hydrochlorination of multi-hydroxylated aliphatic hydrocarbon compounds.
It is also desired to provide a process and apparatus whereby formation of the heavy byproducts such as various ethers of multi-hydroxylated aliphatic hydrocarbon compounds, chlorohydrins, and even higher molecular weight materials such as chlorinated oligomers is minimized.